Lee Smolin's "E8 Unification of Gravity & Yang-Mills Theory

[marcus]

http://arxiv.org/abs/0712.0977
The Plebanski action extended to a unification of gravity and Yang-Mills theory
Lee Smolin
13 pages, one figure
(Submitted on 6 Dec 2007)

"We study a unification of gravity with Yang-Mills fields based on a simple extension of the Plebanski action to a Lie group G which contains the local lorentz group. The Coleman-Mandula theorem is avoided because the theory necessarily has a non-zero cosmological constant and the dynamics has no global spacetime symmetry. This may be applied to Lisi's proposal of an E8 unified theory, giving a fully E8 invariant action. The extended form of the Plebanski action suggests a new class of spin foam models."

 

[MTd2]

HA! He cited Lisi's paper! :D

 

[cristo]

HA! He cited Lisi's paper! :D

I don't see that as all too surprising: Garrett worked at Perimeter for a while with Smolin, didn't he marcus?

 

[MTd2]

I'm not surprised. I'm happy for him.

 

[marcus]

Cristo and MTd2, I think all three of us would say that we are not surprised that Smolin posted a QG framework in which Lisi's work with E8 could fit (and could possibly be brought to successful conclusion). It was clear from Lisi's online ILQGS seminar talk, where Smolin and Ashtekar were asking a lot of questions, that Lee was interested by the E8 business. Maybe you listened to the ILQGS seminar audio---it was a good talk and lots of discussion.

I have to say, though, that I am impressed with how PROMPTLY Smolin came out with this paper and how SOLID the paper is. It puts what Lisi is doing, and how Smolin suggests fitting it into the established QG framework, in a HISTORICAL context and has citations going back to 1957, 1967, 1977 but most interestingly to 1992-1994 work of Peldan. which in some sense FORESHADOWED the kind of unification he is talking about and how he is suggesting that E8 could fit in (if E8 turns out to be the right way to go).
So this paper impresses me because it is solid scholarly work and not shooting from the hip.

It is carefully thought out and carefully worded. It sounds as if Smolin was READY for the E8 thing to happen, so the paper was in some sense already in the mill.

So that part, the timing, I guess does surprise me. I was surprised at how quickly a paper of this caliber appeared.

...Garrett worked at Perimeter for a while with Smolin, didn't he marcus?

Cristo, i actually know very little of the background story to this research. (Not an insider just a observer on the sidelines like many another.)

I remember reading that Garrett was a visitor at Perimeter for a while this fall. That was probably someone else's doing, not Smolin's. There are a lot of energetic people at Perimeter who act more or less independently. Creative people are chosen, but no one person is in control. So somebody invited Garrett to spend a few weeks as a visitor, and while he was there he gave a seminar talk which was well attended. I don't know what, if any, contact Garrett had with Lee during that time. We don't need to know such details although its fun to imagine being a fly on the wall.
Actually Cristo you may know more than I do. Maybe you can fill us in.

 

[MTd2]

So, is there any comment on blogs or elsewhere on the net about this article?

 

[marcus]

So, is there any comment on blogs or elsewhere on the net about this article?

a couple at Woit's blog. I didn't check elsewhere. If you find some please let us know about them!

 

[cristo]

Actually Cristo you may know more than I do. Maybe you can fill us in.

I just conjectured that, since Garrett was at Perimeter, and since both people acknowledge each other in their paper, that they did some work together on it. Of course, I could be wrong.

 

[ccdantas]

So, is there any comment on blogs or elsewhere on the net about this article?

Well, I've recently posted about it http://egregium.wordpress.com/2007/12/07/the-plebanski-action-extended-to-a-unification-of-gravity-and-yang-mills-theory/" . I'm expecting technical comments only. No comments for the moment.

 

[jal]

heheh! I had to check it out.

marcus
It is carefully thought out and carefully worded. It sounds as if Smolin was READY for the E8 thing to happen, so the paper was in some sense already in the mill.

So that part, the timing, I guess does surprise me. I was surprised at how quickly a paper of this caliber appeared.

That is a good reason that Garrett aknowledged input from Smolin.

 

[Coin]

I have to say, though, that I am impressed with how PROMPTLY Smolin came out with this paper and how SOLID the paper is.

Do you suppose that Smolin wrote this paper in the time since Lisi's paper was released? (It is, after all, not very long.) Or do you think that this is maybe something Smolin's been working on in the background for awhile, say since Lisi previewed his work back around Loops '07?

 

[marcus]

I just conjectured that, since Garrett was at Perimeter, and since both people acknowledge each other in their paper, that they did some work together on it. ...

I think you must be right! I had forgotten the reciprocal acknowledgment.

Do you suppose that Smolin wrote this paper in the time since Lisi's paper was released? (It is, after all, not very long.) Or do you think that this is maybe something Smolin's been working on in the background for awhile, say since Lisi previewed his work back around Loops '07?

I think that is a good guess. At the moment my mind is a blank when it comes to understanding how and on what kind of time schedule these people work. I am still impressed by the solidness and carefulness of the paper, but maybe it is not so surprising on second thought.
=================================

the most radical thing in the paper is getting fermions from disordered locality (essentially by an old idea of Wheeler that must have seemed quite outrageous at the time)
in other words Smolin suggests we think of fermions as arising in quite a different way from Lisi.

does anyone have a reaction to this? I imagine it is potentially controversial.

 

[jal]

dumdumtitllydumdum
I wonder if "bee" has something in the works.

 

[grosquet]

A quote from Marcus' thread on Loops '07:
"garrett
06-27-2007, 01:06 AM
Quick post from Mexico:

Wow, I've had more good physics conversations with more people in the past two days than I have in the past ten years. I think my brain's going to explode.

My talk went well -- the E8 idea has attracted a lot of attention. Some quotes to amuse you:
"This is very interesting." -- L.S. "

See https://www.physicsforums.com/archive/index.php/t-164403.html

Also of interest:
https://www.physicsforums.com/showthread.php?t=175261

https://www.physicsforums.com/archive/index.php/t-100984.html

 

[marcus]

Grosquet, thanks for getting links to those past threads! I had forgotten some of what was in them. Interesting stuff. Like the comment on Garrett Lisi's Loops '07 talk back in June.
===============

I am a bit uncertain at this point as to how compatible Lee's paper actually is with what G.L. is attempting. He seems to have a radically different way to obtain the fermions.

It makes me wonder if Smolin's way gets the right fermions, or whether in order to do so it needs the whole E8 or not, does it predict a lot of extra particles that G.L.'s approach doesn't. Or does it predict different particles from G.L.

I would appreciate comment from anyone on this. L.S. use of E8, even if it STARTS with G.L. bosons, seems on the face of it radically different. Or am I missing some simple observation that would restore peace and harmony.

===============
Grosquet, your name sounds like the French antecedent of the American name Crockett. Maybe the famous Davy Crockett was originally of French ancestry.

 

[MTd2]

I found some lenghty discussions about Smolin's paper. Apparently, some people got even more things wrong at his paper, making it seems a pile of ash ( not even the 1st generation is right):

Jacques Distler final disconstruction on Lisi's paper, appealing to Smolin's:

http://golem.ph.utexas.edu/~distler/blog/archives/001505.html#c013319

Comments from Smolin, scroll down all the way:

http://cosmicvariance.com/2007/11/16/garrett-lisis-theory-of-everything/

More comments on Theorem Egregium:

http://egregium.wordpress.com/2007/12/07/the-plebanski-action-extended-to-a-unification-of-gravity-and-yang-mills-theory/

Personal opinion:

http://egregium.wordpress.com/2007/12/11/garrett-and-smolin-to-boldly-go/ It is interesting to note 2 things:

Smolin's credibility is very questioned right now, by some people.

The bloggers found the article here but didnt bother to post any comments here.

 

[marcus]

Comments from Smolin, scroll down all the way:

http://cosmicvariance.com/2007/11/16/garrett-lisis-theory-of-everything/

More comments on Theorem Egregium:

http://egregium.wordpress.com/2007/12/07/the-plebanski-action-extended-to-a-unification-of-gravity-and-yang-mills-theory/
...

Thanks for gathering these links. I hadn't been following all the blog talk, and didn't realize that Smolin had commented at Cosmic Variance. For people who don't want to scroll down looking for it, here is a direct link to Smolin's comment:
http://cosmicvariance.com/2007/11/16/garrett-lisis-theory-of-everything/#comment-306189
I found it interesting, with a fair amount of detail I hadn't seen before.

Here is a direct link to Smolin's briefer comment at Christine's Theorema Egregium blog
http://egregium.wordpress.com/2007/12/07/the-plebanski-action-extended-to-a-unification-of-gravity-and-yang-mills-theory/#comment-2586

 

[Coin]

Hm, the technical discussion at those Theorem Egregium posts is pretty great.

Smolin's credibility is very questioned right now, by some people.

Well... it honestly seems likely to me that there were people who were just looking for some excuse to denounce Smolin, for example because they don't agree with his opinions on string theory etc. I mean, one always has to be very cautious when saying such things, every crank in existence uses the "you're just saying that because you're all against me!" defense at some point. But the thing is, given how relatively modest Lisi's approaches on this subject so far has been-- one preprint of a paper on the Arxiv, the most audacious thing about it being some silly puns in the title-- and how loose Smolin's connections to all this are, I find it difficult to believe that anyone who seriously uses anything about this episode to "question Smolin's credibility" was really giving Smolin or his ideas a fair hearing to begin with.

The bloggers found the article here but didnt bother to post any comments here.

It is a general truth that people are not as likely to post in a forum (where you have to register) as on a blog (where you don't).

 

[marcus]

Hm, the technical discussion at those Theorem Egregium posts is pretty great.
...

I bet Christine will be glad to hear that

The bloggers found the article here...

That's interesting. I know Christine regularly visits here, but i wouln't have guessed that Sean Carroll of CVblog, or Jacques Distler of Musing blog, got news of Smolin's article from us! If they did, I must have missed it.

Don't worry if bloggers don't always join the PF discussion when they come by here and see some news. They naturally want to go home and inject energy into their own blog, and discuss things (perhaps including the new paper) with their own circle of regulars.

 

[ccdantas]

Smolin's credibility is very questioned right now, by some people.

?

I don't think so. Certainly Distler raised a serious point in Lisi's work which should be addressed. But whatever this point leads to -- I think there is a lot to be learned with what Lisi (and others in the same line) are attempting.

Smolin's paper, as far as I can understand it, advances other issues and makes use of Lisi's work as an application. What about the extended Plebanski action he proposes? This is interesting enough for me. I want to learn more about it. But it seems it is not raising much attention.

Now, the fact that Smolin acknowledges Lisi's work and uses it at some extent in his formulation does not mean much. Smolin acknowledges in his paper that there are still many open issues to be addressed in Lisi's work. If it proves to be wrong, does it prove that Smolin's formalism is wrong as well?

 

[ccdantas]

I bet Christine will be glad to hear that

Great to know!

 

[Coin]

Now, the fact that Smolin acknowledges Lisi's work and uses it at some extent in his formulation does not mean much. Smolin acknowledges in his paper that there are still many open issues to be addressed in Lisi's work. If it proves to be wrong, does it prove that Smolin's formalism is wrong as well?

Actually no. If you look at Smolin's paper in the main part he does not even use E8 in specific. He has an argument which he bases on "some gauge group G", and although he specifically notes that group might be E8 there are of course other possible candidates for G as well.

EDIT: Or did I misunderstand your question?

 

[ccdantas]

Actually no. If you look at Smolin's paper in the main part he does not even use E8 in specific. He has an argument which he bases on "some gauge group G", and although he specifically notes that group might be E8 there are of course other possible candidates for G as well.

Right, that is what I mean. The answer appears to be NO. It appears to me that Smolin's formalism is quite a general one, and independent of the use o E8. That is one of the questions that I have raised in my blog.

EDIT: I copy here:

" From a first reading of Smolin’s paper, the most interesting aspect of it (as I see it) appears to be the introduction of an extension of the Plebanski action that accepts any large group structure (containing the local Lorentz group), showing that, with a symmetry breaking mechanism, the resulting dynamics is that of a unified Einstein-Yang-Mills, plus corrections. Smolin suggests his framework could be used for building up the dynamical sector of Lisi’s proposal (by applying the group E8 in the proposed extended action), a part of Lisi’s work that has not been worked out satisfactorily. "

 

[Coin]

Ah, okay. Sorry, I had seen the post at Theorem Egregium but I hadn't realized until after that last post that that was you...